Membrane guard for a membrane electrode cell

ABSTRACT

A guard for a membrane electrode cell in an electrocoat paint system that separates the counter-electrode, the object being painted, from the membrane shell housing that surrounds the electrode, which is located inside the membrane. The guard is of a grid-like structure with openings that have rounded edges and allows for the flow of electricity between the electrode and the counter-electrode and for a substantially continuous flow of paint particles around the membrane electrode cell. The guard is made from a durable, flexible, non-conducting material that is impervious to the temperature conditions and acids, solvents and other compounds often found in electrocoating paint baths. Embodiments of the present invention include an externally affixed guard, an integral guard and a rigid membrane guard.

This is a continuation of application Ser. No. 08/066,991 filed on May24, 1993, now abandoned and which is a continuation of application Ser.No. 07/678,733 filed on Apr. 1, 1991 now U.S. Pat. No. 5,213,671.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a membrane electrode cell system usedin electrocoating, and more particularly to a membrane guard for amembrane electrode cell in an electrocoating paint system.

1. Description of the Prior Art

Electrocoating is broadly classified into two categories, anionic, usinganionic paints, and cationic, using cationic paints. Both of theseprocesses are commercially used to deposit paint films on varioussubstrates. As used herein, electrocoating and electrodeposition areconsidered interchangeable terms.

Membrane electrode cells are commonly used in electrocoating systems andprimarily serve two functions. The first function of the membraneelectrode cell is to act as the opposing electrode in the electrocoatingprocess, with the object being painted serving as the counter-electrode.The second function is to serve much like a dialysis cell orelectro-chemical cell in which ions are removed from the paint bath tomaintain proper paint bath chemistry. The membrane electrode cell canhave many shapes, and often is shaped as a flat rectangle, semi-circle,tube or cylinder. An electrocoating process employing such a membraneelectrode cell is disclosed in U.S. Pat. Nos. 4,851,102, 4,711,709 and4,834,861, which are hereby incorporated by reference.

The membrane used in a membrane electrode cell can be eitherion-exchange or neutral. It often is comprised of a composite of resin,binder, and flexible substrate, and typically is rather fragile andsusceptible to damage. An example of an anion-selective membrane isModel Number MA3475, manufactured by Sybron Chemical, Inc. An example ofa cation-selective membrane is Model Number MC3470, also manufactured bySybron Chemical, Inc. An example of a neutral membrane is Cellgard ModelNumber 5511, manufactured by the Celanese Corporation.

The membrane is arranged in such a fashion as to separate theelectrocoating paint bath from the electrode. An electrolyte fluid flowsbetween the inside of the membrane and the outside of the electrode.This electrolyte fluid, which is comprised mostly of deionized water anda small amount of acid or amine (depending on the type of electrocoatingemployed), is responsible for flushing the ions that pass through themembrane into the membrane electrode cell from the paint bath. Theconductivity of this electrolyte fluid usually is maintained in therange of 500 to 2,000 microSiemens/cm (microMho/cm).

The flow of electricity from the electrode to the counter-electrode mustpass through the electrolyte fluid, membrane, electrocoating paint bathand eventually the deposited paint film. If the resistance of any ofthese elements increases, then the driving voltage generally must alsobe increased to maintain the same flow of current. The thickness of thedeposited paint film (typically 0.5 to 1.5 mils) is directly related tothe number of coulombs (ampere/seconds) that pass between the electrodeand counter-electrode. Therefore, any reduction of the flow ofelectrical current results in a reduction in the rate of paint filmdeposition. Typical driving voltages are between 150 and 350 volts. Oncethe voltage goes higher than a certain level, paint film defects canoccur from "rupture" where tiny air bubbles trapped in the film cause arough film appearance.

A recurrent problem for most electrocoating systems is the loss ofcounter-electrodes from the conveyor hooks that move them in and throughthe paint bath. Some electrocoating systems paint a wide variety ofsizes and shapes of counter-electrodes. Often the hooks either are notoptimally designed for each and every different counter-electrode, orthe counter-electrodes are incorrectly hung on the hooks. In any event,as the counter-electrodes enter the paint bath, the buoyant forcescaused by the immersion of the counter-electrode into the paint bathsometimes lift them off of the hooks, and the release of trapped airfrom inside the counter-electrode can cause wild swings back and forth.The combination of these movements with the conveyor motion and/or paintbath agitation often causes the loosened counter-electrode to fallcompletely off the hook. In some cases, a trailing counter-electrodethat is on a hook directly behind the loose counter-electrode can alsobecome entangled and cause successive counter-electrodes to pile up,much like an automobile chain collision.

As counter-electrodes come loose and fall off their hooks, they can comeinto physical contact with the membrane electrode cells that generallyare arrayed along the long sides of the paint bath tank. Also,maintenance personnel sometimes use long-handled grappling hooks toremove the fallen counter-electrodes and either the grappling hook orthe retrieved counter-electrode can come into contact with the membraneelectrode cell. Since the membrane can represent up to about 90 to 95%of the exposed surface area of the membrane electrode cell, it isespecially vulnerable to physical damage if any object comes into directphysical contact with the membrane electrode cell.

If the membrane suffers a cut, puncture, hole or rip, then itsfunctionality can be severely and adversely affected. Once an opening,or "short-circuit" path, through the membrane is created, the membraneno longer can effectively remove ions or easily allow the passage ofcurrent to the counter-electrode, thereby impeding or stoppingaltogether the electrocoating process. Two things occur almostimmediately after a membrane is penetrated by a counter-electrode orother object. The first is that the electrolyte fluid becomescontaminated with paint. Since the paint particles carry the same chargeas the electrode, they are repelled by the electrode. With no ready wayout, these paint particles attempt to escape through the membrane. Thisoften results in the deposition of the paint particles on the innersurface of the membrane because they are too large to migrate throughthe small passages of the membrane. This phenomena "fouls" the membrane,and the resistance of the membrane can dramatically increase.

The second problem occurs thereafter. With the membrane fouled, it nolonger effectively removes ions from the paint bath. With theion-removal process disrupted, the chemical balance of the paint tank issoon upset.

Over the years many attempts have been made to decrease the incidence ofdamaged or compromised membranes. Polyvinyl chloride (or "PVC") pipes,sometimes called rub rails, have been positioned between the membraneelectrode cell and the counter-electrode. If a counter-electrode swingsfrom side-to side, then these rub rails tend to keep thecounter-electrode from contacting the membrane electrode cell. Normally,two or three rub rails are equally spaced vertically between the top andthe bottom of the counter-electrode. While rub rails do offer somedegree of protection, the size and shape of counter-electrodes vary to ahigh degree, limiting the effectiveness of this approach. Moreover, itis not practical to put rub rails throughout the paint bath, since thiswould block the free-flow communication of paint and electricity betweenthe electrodes and also physically reduce the working volume of thepaint bath. A further disadvantage of rub rails is that membranes canstill be damaged if corners or sharp edges of certain counter-electrodespass in between or around a rub rail and collide with the membrane.

Another method of preventing physical contact with the membraneelectrode cell employs non-conductive, perforated barriers (materialsuch as PVC or fiberglass) that may be as much as 1 inch deep with 1inch by 1 inch openings. This method overcomes some of the problemsassociated with the PVC rub rails in that the network of openings in thebarrier can be smaller than the gaps between the PVC rub rails. Adisadvantage of this method, however, is that the depth and relativelylarge exposed surface area of the barrier create a significantdisruption to the free-flow communication and circulation of the paint.

A high percentage of the electrocoat paint bath is water. The remaindermostly is paint resin, pigment, neutralizer and solvent. The paint bathmust be vigorously agitated on a substantially continuous basis or thepaint particles will tend to fall out of solution and gather at thebottom of the tank. Hence, any object inside the tank that presentsitself as a significant flow or circulation restrictor, especially onewith flat, horizontal or vertical surfaces, will tend to cause paintparticles to fall out of solution and also disrupt the even and orderlylines of current between the electrode and the counter-electrode. Ifthese paint particles begin to coagulate, they can start to gather andpile up on any flat ledges or openings of any protective barrier. Ifleft unchecked, the coagulated particles can "grow" to a level wheresmall, semi-hardened pieces can flake off. These coagulated paintparticles can then settle out on the counter-electrodes and cause amyriad of paint film defects. Once paint particles begin to coagulate,the task of getting those paint particles back into solution can be acostly and time consuming undertaking. In addition, the driving voltagemust be higher than otherwise to overcome the restrictions to the flowof electrical current caused by this kind of protective barrier, whichis less efficient in terms of energy consumption and paint bath cooling.

Large diameter PVC pipes with numerous holes (typically 1/2 to 3/4inches) drilled in them have also been used in an effort to protect themembrane. The membrane electrode cell can be placed inside of thesepipes, offering some degree of protection. This method suffers, however,from the same drawbacks of the external barriers. The wall thickness ofthe large diameter (say 4 or 6 inches) pipes can be as much as 0.432inches. Once a hole is drilled through the pipe and it is then placed ina vertical position, the bottom side of the hole acts as a ledge. As theundrilled portions of the pipe act as a flow restrictor to the free-flowof paint, small amounts of paint particles fall out of solution andsettle on this ledge. The undrilled portions of the pipe also act todisrupt the free-flow communication of the current much like other priorart barriers.

Yet another structure has been fabricated from large flat sheets made ofnon-conductive material (such as PVC or what is known in the industry bythe trademark Nylon). One prior art structure covered a planar electrodewith a flat steel grill coated with a plastic material. Many holes (say1/4 to 3/4 inches) or other perforations are drilled or cast into theflat sheet or grill. This sheet may be as thick as 1/2 inch. Thesestructures, like the drilled PVC pipe, offer some protection for themembrane, but they also suffer from the same disadvantages discussedabove. Moreover, the plastic coated steel grill structure suffers fromseveral additional drawbacks. The plastic coating can be scratched ornicked, providing a site for paint deposition. Because the painttypically does not cure, it eventually falls off, resulting in paintfilm defects. Further, the conductivity of the steel in the grill posesundesirable electrical isolation problems.

Another method for protecting the membrane electrode cell involves theuse of a non-conducting mesh material wrapped around the membrane. Thismesh has much smaller openings than discussed above and is used in sucha way that the mesh makes direct contact with the membrane. While themesh does offer some protection for the membrane, it has severaldrawbacks. For example, since the mesh makes direct contact with themembrane, some of the membrane passages are completely blocked off,thereby reducing the efficiency of the membrane. In addition, the meshcan inadvertently chafe or abrade the membrane at the contact points,resulting in damage to the membrane. Moreover, paint particles can buildup on the horizontal surfaces of the mesh where the mesh makes contactwith the membrane.

Another version of this approach uses long slender, rectangular-crosssection, non-conducting pieces with small inter-connecting supportsarrayed to form a grill completely over the membrane. Since the supportsused in this approach also come in direct contact with the membrane, itsuffers from the same disadvantages. Another drawback to this approachis that, since the grill is mostly one-directional, in some instances itcan act as a guide or channelling mechanism and directcounter-electrodes or other objects into contact with the membrane.

Even though these prior methods more or less offer some protection forthe membrane electrode cell, they all create drawbacks that ultimatelycan be just as serious as the damage caused when a membrane ispenetrated. Hence, it is desirous to develop a guard that protects themembrane, but does not disrupt the free-flow communication of paintparticles or electrical current vital to a properly-functioningelectrocoating system.

SUMMARY OF THE INVENTION

The present invention overcomes the aforementioned disadvantages of theprior art. The general object of the present invention is to provide aguard system that is externally affixed to or integral with a membraneelectrode cell and that is capable of offering significant protectionfor the membrane while maintaining free-flow communication of the paintand electrical current in the paint bath. The present invention isparticularly applicable to membrane electrode cells of cylindrical ortubular shape. The guard of the present invention can be of smalldiameter (such as approximately 3 inches) and of a shape or profileconducive to flow of paint particles around and through the guard. Paintparticles can more readily slip around a curved object as opposed to arectangular or planar object such as is the case with rectangular formsof membrane electrode cells or with prior art barriers. In addition, thepresent invention provides a concentric and tubular guard that is formedaround a membrane electrode cell of a smaller diameter but which sharesthe same centerline.

Another object of the present invention is provide even higher levels ofdurability by combining a rigid membrane structure along with a guardfor even greater protection.

Yet another object of the present invention is to provide a light-weightand flexible guard and membrane cell structure that readily deflectsand/or absorbs the impact energy of a counter-electrode or other object.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned features and objectives of the present inventionwill become more apparent by reference to the following descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a vertical fractional view illustrating an externally affixedembodiment of the present invention;

FIG. 1A is an expanded view of a portion of the embodiment illustratedin FIG. 1;

FIG. 2 is a vertical fractional view illustrating an integral embodimentof the present invention;

FIG. 2A is an expanded view of a portion of the embodiment illustratedin FIG. 2;

FIG. 3 is a fractional view illustrating an embodiment of the membraneguard of the present invention;

FIG. 4 is a section view of the membrane guard shown in FIG. 5;

FIG. 5 is a vertical fractional view illustrating a rigid membraneembodiment of the present invention;

FIG. 5A is an expanded view of a portion of the embodiment illustratedin FIG. 5;

FIG. 6 illustrates a rigid membrane assembly and

FIG. 6A is an expanded view of the assembly illustrated in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Detailed description will hereunder be given of embodiments of thepresent invention with reference to the drawings.

In FIGS. 1, 2 and 5, a fractional view of only one half of a tubular orcylindrical membrane electrode cell is shown in a vertical position,which would be disposed in an aqueous solution for electrocoating. Theelectrode, electrical connection, electrolyte fluid supply line and itsconnection are not shown, but such elements can be arranged such asdescribed in U.S. Pat. Nos. 4,711,709 and 4,834,861. The membraneelectrode cell may also include other elements which are described inthese patents. While the preferred embodiment of the present inventionis a guard for tubular or cylindrical membrane electrode cells, thepresent invention can be applied to a variety of shapes of membraneelectrode cells. It is noted that with tubular or cylindrical membraneelectrode cells, the surface area of the guard is significantly greaterthan the surface area of the electrode. Thus, the flux density is lowerat the guard than at the surface-of the electrode, resulting in betterefficiency (because of more open surface area) than planar barrierswhere the surface area ratio of the guard to the electrode essentiallyis one to one.

The present invention is useful with components that are consolidatedover what was disclosed in U.S. Pat. No. 4,711,709. Without limiting theapplicability of the present invention, cap 12 generally corresponds tosecond insulating tube 6, rubber packing 11, waterproof cap 12, and band9B shown in FIG. 1 of U.S. Pat. No. 4,711,709. Similarly, collar 14generally corresponds to first insulating tube 5 and band 9A shown inFIG. 1 of U.S. Pat. No. 4,711,709.

In FIGS. 1 and 1A, guard 10 is externally affixed to membrane shell 1.Guard 10 is made from a durable, non-conducting material that isresistant to attack from chemical agents, temperature, and most impactforces found in electrocoating paint baths. Guard 10, as well as guard15 (FIG. 2) and rigid form 18 (FIG. 6), can be fashioned from athermoplastic such as polyethylene (low, medium or high densityversions), polypropylene, Nylon or PVC. Guard 10 is fashioned in such amanner that its inside diameter snugly fits over collar 14 and cap 12.Guard 10 can be firmly attached to either collar 14 or cap 12 or both bymeans of applying a common chemical-resistant epoxy or by using a PVC orother appropriate weld.

Porous tube 2 is made from a reticulated, flexible, non-conducting,durable, chemical and heat resistant material and is fashioned to theproper length. Porous tube 2, which is permeable to both water andelectrical current, separates collar 14 and cap 12 and acts as amembrane support member. Porous tube 2 is made with such an insidediameter that it forms a snug fit over the outside diameter of the innerlip of both collar 14 and cap 12. Neck 5 is glued into collar 14.Overflow nozzle 7 is provided to allow passage of electrolyte fluid outof membrane shell 1 (FIG. 1). Membrane 6 is disposed in a form toencircle the outer circumference of porous tube 2 with cloth 4A insertedin between to form an intermediate layer. Outer cloth 4B covers theouter surface of membrane 6 by forming an encircling layer. Cloths 4Aand 4B are made from chemical fibers and are water permeable as well assufficiently durable against tensile force. Collar 14 and cap 12 areassembled to the structure by using chemical-resistant epoxy 16.Generally, the materials used in the construction of membrane shell 1are all of a non-conducting synthetic thermoset or thermoplasticmaterials such as polyethylene, polypropylene, Nylon or PVC, and ensuresan inert, durable, lightweight and flexible shell structure. Membraneshell 1 houses the membrane around the electrode and provides waterpassage 3 around the electrode (not explicitly shown).

Gap 8 between cloth 4B and the inner surface of guard 10 can be anysuitable width conducive to paint flow in and around guard 10, and inthe preferred embodiment is in the range of about 0.3 to 0.4 inches.Porous tube 2, membrane 6 and guard 10 all share the same centerline andhave a substantially fixed concentric relationship. They are thusself-centering, and gap 8 is substantially the same at all points aroundthe circumference of membrane 6. Gap 8 allows for flow communication ofthe paint particles in and around and through guard 10 while minimizingthe coagulation of paint particles common with prior art barriers. Thereticular feature of guards 10 and 15 (also see FIG. 3 and FIG. 4) andguard 15 provides a substantial amount of open space, which can be up to50% or more, and still have enough tensile strength to remain intactafter an object makes physical contact. Since guards 10 and 15 areflexible, some of the durability is attributable to the fact that theguard can absorb most impacts. While guard 10 or guard 15 may bend ordeform slightly under stress, it generally returns to its originalshape.

FIGS. 2 and 2A illustrate an embodiment of the present invention inwhich guard 15 is an integral part of the assembly of membrane shell 1.With the exception of guard 15 and gap 9, the elements of FIG. 2, andthe reference numerals therefor, generally are the same as in FIG. 1. Inthis embodiment, guard 15 is fashioned to the proper length andassembled integral with porous tube 2, inner cloth 4A, membrane 6, andouter cloth 4B. The outside diameter of guard 15 is such that it forms asnug fit with the inside diameter of the outer lip of both collar 14 andcap 12. Gap 9 generally is established by the difference between theinside diameter of guard 15 and the outside diameter of cloth 4B, whichgenerally is established by the outside diameters of membrane 6, cloth4A and porous tube 2. By appropriate selection of the materialdiameters, gap 9 can be any of a variety of widths, and in the preferredembodiment is in the range of 0.1 to 0.15 inches and allows flowcommunication of the paint particles through and around guard 15. Aswith the embodiment shown in FIG. 1, gap 9 is substantially the same atall points around the circumference of membrane 6 due to theself-centering and substantially fixed concentric relationship of guard15, membrane 6 and porous tube 2.

Both guards 10 and 15 do not substantially impede the flow of electricalcurrent from the electrode to the counter-electrode. The preferredembodiments of guards 10 and 15 are shown in FIG. 3. The high percentageof open area, combined with the small physical size and narrow profileof the interconnecting network (see FIG. 4) do not substantiallyrestrict the lines of electrical current 30. Openings 26 aresubstantially elliptical in shape (approximately 0.275 inches and 0.175inches along the axes of the ellipse in the preferred embodiment) andwhen viewed in the section view (FIG. 4) horizontal connecting elements27 are circular or oval in shape and without sharp corners, planarshapes or other flat profiles. When guards 10 and 15 are viewed in thehorizontal section view (not explicitly shown), vertical connectingelements 28 are also oval or circular in shape and without sharpcorners, planar shapes or other flat profiles. In the preferredembodiment, connecting elements 27 and 28 are approximately 0.1 inchesin thickness.

The combination of these complex, curved profiles reduce the number ofpotential sites where paint particles 32 might coagulate on guards 10 or15. There are no flat ledges or corners and the flow communication isstrong, which results in substantial turbulence around, in and throughguards 10 and 15, which tends to keep the paint particles in constantmotion.

In other embodiments of the present invention, shims or spacers (notexplicitly shown) also are provided to control gap 8 (FIG. 1) or gap 9(FIG. 2). For example, gap 8 can be widened by placement of one or moreshims or spacers between guard 10 and collar 14 and cap 12, and gap 9can be widened by placement of one or more shims or spacers betweenguard 15 and cloth 4B or narrowed by placement of one or more shims orspacers between guard 15 and collar 14 and cap 12.

Another embodiment of the present invention is illustrated in FIGS. 5,5A, 6 and 6A. In this embodiment, the guard structure also serves as thesupporting structure for the membrane materials. Rigid membranestructure 17 is fashioned to the proper length and assembled to collar14 and cap 12 by using chemical-resistant epoxy 16. Rigid membranestructure 17 is further illustrated in FIG. 6. Rigid form 18 is formedby a reticulated, durable, flexible, chemical and temperature resistantmaterial such as used for guard 10 and guard 15. Membrane resinparticles 20 are cast into the openings of rigid form 18 and held inplace by using binder 22, which in the preferred embodiment is amaterial such as polyvinylidene fluoride, sometimes sold under the tradetrademark Kynar. The spacing of adjacent connecting members of rigidform 18 and their higher profile (as compared to membrane resins 20 andbinder 22 cast in between) are such that an errant counter-electrodewill strike it first and absorb the shock, thus avoiding damage to resinparticles 20 or binder 22.

While FIG. 6 illustrates rigid form 18 with openings that aresubstantially in the shape of a diamond, other opening profiles (such asthe ellipses shown in FIG. 3) are used in other embodiments. Resinparticles 20 and binder 22 are cast into the openings of rigid form 18and substantially fill any sharp corners and eliminate ledges associatedwith rigid form 18.

In other embodiments of the present invention, rigid membrane structure17 of FIG. 5 is substituted for porous tube 2, cloths 4A and 4B andmembrane 6 of FIGS. 1 and 2, and combined with guard 10 of FIG. 1 andguard 15 of FIG. 2, respectively. In these embodiments, a double guardedstructure is produced whereby guard 10, or alternatively guard 15,protects the already durable rigid membrane structure 17.

Similarly, in other embodiments of the present invention, guards 10 and15 are utilized with other membrane structures, such as a membranecomprised of resins in a unitary, semi-rigid binder. In theseembodiments, guards 10 and 15 typically are attached only at one point(either at collar 14 or cap 12) because these unitary membranestructures typically swell as water is absorbed. Attaching at only oneend of the guard allows the guard to be "floating" with respect to themembrane structure, thereby accommodating any dimensional changes in themembrane structure.

In still other embodiments of the present invention, the guardedmembrane electrodes (such as shown in FIGS. 1, 2 and 5) are, forexample, placed horizontally in the paint bath tank and combined withvertical rub rails or other prior art barriers for added membraneelectrode protection.

While the present invention has been described in terms of preferred andalternative embodiments, it will be obvious to one skilled in the artthat many alterations and modifications may be made withoutsubstantially departing from the spirit of the invention. Accordingly,it is intended that all such alterations and modifications be includedin the spirit and scope of the invention as defined by the appendedclaims.

We claim:
 1. A membrane electrode cell for electrocoat painting of acounter-electrode, comprising:a tubular membrane structure having aninner surface and an outer surface, wherein at least a portion of theouter surface of the tubular membrane structure comprises a membranehaving an outer surface; an electrode disposed substantially within thetubular membrane structure, wherein the electrode is positioned withinthe tubular membrane structure in a manner to allow passage of aflushing fluid between the electrode and the inner surface of thetubular membrane structure; and a tubular guard having an inner surfaceand an outer surface, wherein the tubular membrane structure andelectrode are positioned within the tubular guard in a substantiallyconcentric manner wherein the tubular guard may serve to preventphysical contact between the counter-electrode or other object and theouter surface of the tubular membrane structure, wherein the tubularguard is comprised of a non-conductive material and has a plurality ofopenings in the surface thereof, wherein the openings have substantiallycurved surfaces along portions of the periphery thereof.
 2. The membraneelectrode cell of claim 1, wherein the openings in the tubular guard aresubstantially in the shape of an oval.
 3. The membrane electrode cell ofclaim 1, wherein the openings in the tubular guard are substantially inthe shape of a circle.
 4. The membrane electrode cell of claim 1,wherein the openings in the tubular guard are substantially ofelliptical shape.
 5. The membrane electrode cell of claim 4, wherein theellipse of the openings is approximately 0.275 inches in length alongone axis of the ellipse and approximately 0.175 inches in length alongthe other axis of the ellipse.
 6. The membrane electrode cell of claim1, wherein the tubular guard is concentrically positioned around themembrane structure to define a substantially uniform gap.
 7. Themembrane electrode cell of claim 6, wherein the gap is in the range ofabout 0.1 to 0.15 inches.
 8. The membrane electrode cell of claim 6,wherein the gap is in the range of about 0.3 to 0.4 inches.